The present invention relates to an optical fiber connector for connecting an optical fiber wire (core, clad sections) to another optical fiber wire according to a fixed type connecting technique or a detachable type connecting technique.
A first conventional technique for connecting an optical fiber wire to another optical fiber wire is a fusion-bonding technique, in which the axes of the optical fiber wires are aligned with each other at their butted portions, and the butted portions of the optical fiber wires are fused in the form of a fusion bonding. A fusion-bonding device is used for this technique. A second conventional technique is a fixed type connecting technique, in which optical fiber wires to be connected are embedded in advance within a fitting provided in a connection passage of the optical fiber wires, and the optical fiber wires are mechanically fixed by filling up an oil material, a grease material, an epoxy resin material, or a state-of-the-art gel material in the connection space. A splicer or an optical distributor is used for this technique. A third conventional technique is a detachable type connecting technique, in which a ferrule is fitted to each end of optical fiber wires, and the optical fiber wires are mechanically butted through an adapter to be joined each other. An optical fiber connector is used for this technique. In order to reduce connection loss, some optical fiber connector uses a lens, an oil material, a grease material, or a state-of-the-art gel material in the connection space. (For example, Japanese Patent Laid-Open Publication No. Sho 56-110912 discloses an optical fiber connector using a lens, Japanese Patent Laid-Open Publication No. Sho 56-081807 disclosing an optical fiber connector using an oil material, and Japanese Utility Model Publication No. Hei 04-043841 disclosing an optical fiber connection using a gel material.)
Fundamental requirements for connecting optical fiber wires are as follows.
i) Two optical passages (cores) to be connected are positioned on the aligned axes of the optical fiber wires;
ii) The connection space is strictly small; and
iii) The retaining mechanism is capable of preventing any invasion of foreign materials such as dust, vapor or water.
From this point of view, the conventional connecting techniques have the following disadvantages.
The first conventional technique or fusion-bonding technique satisfies the above three fundamental requirements. However, it is not detachable type, and thereby cannot be used as a connector.
In the second conventional technique or fixed type connecting technique, it is required to employ a complicated mechanism and take a number of assembling hours for fabricating and aligning the embedding portion of the optical fiber wires to satisfy the above fundamental requirements. In addition, the oil or grease enclosed in the connection space is inevitably run out or oxidized. The epoxy resin is not run out but inevitably oxidized. This technique is not detachable type, and thereby cannot be used as a connector, resulting in limited application.
The third conventional technique or detachable type connecting technique uses the structure in which the ferrule is fitted to each end of the optical fiber wires, and the optical fiber wires are mechanically butted through an adapter to be joined each other. Thus, as compared with the first and second conventional techniques, this technique cannot satisfy the first and second fundamental requirements, and thereby the optical transmittance is inevitably reduced. While various polishing, such as planar surface polishing, spherical surface polishing, or inclined surface polishing, has been applied to the end of the optical fiber wire to suppress this optical attenuation and improve the optical transmittance, the above first and second fundamental requirements are not sufficiently satisfied.
The present invention provides an optical fiber connector capable of satisfying the aforementioned three fundamental requirements. A typical optical fiber connector includes FC-type and SC-type specified in JIS. While they have a difference in coupling arrangement, they commonly rely upon the machining accuracy of the ferrule and adapter to align the axes of optical fiber wires.
For example, in the FC-type optical fiber connector, or an optical fiber connector for single mode optical fiber wires, on the assumption that each of optical fiber wires has a standard dimension or size, a ferrule to be fitted to the optical fiber wire has an outside dimension of 2.4995 mm with its tolerance of xc2x10.0005 mm, and a hole for passing the optical fiber wire therethrough and having a diameter of 0.125 mm, in which the tolerance of the concentric circle with respect to the hole is limited to xc2x10.0014 mm. Further, an adapter for inserting the ferrule thereinto has an inner diameter of 2.501 mm with its tolerance of +0.003 mm. The ferrule and the adapter are coupled by a connection nut with guiding them along two key grooves formed at a ferrule holder and the adapter, respectively.
The connector is made with these accurate numerical values. However, each connection loss actually measured at both ends of the connector exhibits a significantly different value. Specifically, provided that one end xe2x80x9caxe2x80x9d of both ends of a single optical fiber connector is an entrance (transmit section) and the other end xe2x80x9cbxe2x80x9d is an outlet (receive section), each of the ends is connected to a master cord. When comparing the connection loss in case of using the end xe2x80x9caxe2x80x9d as a junction with the connection loss in case of using the end xe2x80x9cbxe2x80x9d as a junction, the difference is up to about 0.15 dB. This is caused by the displacement with respect to the axes of the optical fiber wires and the optical attenuation in the connection space. By way of experiment, when using a rotatable adapter and measuring with rotating the ferrule, the difference between the above connection losses was reduced in all of 20 samples. This proves that the difference is caused by the displacement with respect to the axis. The conventional optical fiber connectors do not have any mechanism for correcting such displacement with respect to the axes of the optical fiber wires.
In order to solve the aforementioned first problem, a mechanism for correcting such displacement with respect to the axes of the optical fiber wires is achieved by making a ferrule holder rotatable, and providing in the adaptor a mechanism for stopping the rotation of the ferrule holder at a optimum value with measuring the connection loss and retaining the ferrule holder.
A connection space inevitably exists at the junction of two optical fiber wires, i.e., between opposed ends of the optical fiber wires. While the oil or grease has been used to minimize this space, this application is limited due to its functional drawback, such as running out or oxidization. In order to solve the second problem, a transparent silicone low crosslinking-density gel having a refractive index substantially equal to that of the optical fiber wires is filled in the connection space to use as a junction conductor.
The composition and physical property of the silicone low crosslinking-density gel are as follows.
1. Composition: silicone mixture
2. Refractive index: 1.465 xc2x10.005
3. Viscosity: between 100,000 cP or more and 150,000 cP inclusive or less
4. Appearance: transparent
5. Temperature: usable in the range of xe2x88x9220xc2x0 C. to 120xc2x0 C. substantially no variation at room temperature
6. Water absorbing property: water absorption to the composition is 0.1% or less
7. Hygroscopic property: substantially no hygroscopic property to the composition
8. Anti-dust: dust may attach to the surface, but does not penetrate into the composition
9. Pressure resistance: freely deformable to pressure
10. Vibration resistance: no separation or no disassembly
11. Chemicals resistance: insoluble to most solvents
12. Oxidation: inoxidizable
13. Liquidity: illiquidity, deformable to pressure
14. Period for performance guarantee: over 20 years at room temperature
The basic model of the conventional optical fiber connectors is the FC-type for indoor use, and a retention mechanism is added depending upon application. For example, a water-resistant optical fiber connector uses a sealing material applied over the external of the FC-type. To solve the third problem, the aforementioned silicone low crosslinking-density gel is used in the junction of two optical fiber wires as a junction conductor. For example, in the FC-type, the silicone low crosslinking-density gel is enclosed in the connection space of the optical fiber wires fitted with the ferrules for connecting to the adapter. This can provide an all-weather optical fiber connector having an optical transmittance of 99% or more and a connection loss of 0.02 dB for any variation of external environment without any change of the size of the connector or any additional structure or mechanism.